1. Field of the Invention
This invention relates to a sheet metal pulley and a means for securing the pulley to an end of a rotary shaft. In particular, the invention concerns a device in which the peripheral surface of a pulley, a web, and a hub portion for affixing the pulley to the end of the rotary shaft of the pulley according to the invention are all integrally formed of a single sheet of metal.
2. Description of the Prior Art
In a conventional installation in which an end of a rotary shaft is to be affixed to a pulley which is integrally formed from sheet metal in one piece, a hub (or boss) portion is formed into a cylindrical shape by deep drawing for the purpose of receiving the shaft end. Such an arrangement is disclosed, for example, in Japanese Patent Publication No. 35779/1981. The shaft is placed in the deep-drawn cup-shaped hub, whereby the pulley is aligned perpendicular to the axis of the shaft. The function of the drawn hub is to provide a contact area extending over the shaft end and along the axis of the shaft adjacent the end, thereby to prevent flexing of the pulley with respect to its correct perpendicular alignment.
After a thin sheet of metal is subjected to deep drawing for formation of the cylindrical configuration, the plate thickness of the cylindrical portion necessarily becomes even thinner. Therefore, when affixing an end of a shaft to the pulley, for example by inserting a locking bolt axially into the bottom of the cylindrical portion of the pulley, the bottom portion is often broken because it has been stretched too thin to bear the load to which it is subjected by the locking bolt. The strength of the walls of the cylindrical portion is also deteriorated by such drawing to the point that the walls cannot hold the peripheral surface of the shaft adjacent the end such as needed to steadily support the pulley on the shaft. The conventional apparatus for endwise affixing a shaft and a one piece pulley, characterized by these defects, is not sufficiently strong and is not satisfactory.
In some apparatus the hub portion of a sheet metal pulley is provided with a claw piece which is cut away and raised by one end in the axial direction such as to fit around the outer peripheral surface of the shaft end at a point axially spaced from the web of the pulley. This is disadvantageous in that the distal end of the raised claw piece is free and can be easily displaced from the shaft. Therefore, the pulley and shaft are not as rigidly and permanently affixed as they could be. The strength of attachment needed for steadily and securely holding the shaft end under loads is lacking in this apparatus as well.
In yet another known apparatus the hub portion is composed of two stacked plates in order to increase the length of axial support for the pulley and to improve the strength of the shaft end installation. This is unnecessarily expensive in both material and assembly requirements.